W3C home > Mailing lists > Public > semantic-web@w3.org > February 2009

Re: live meaning and dead languages

From: Frank Manola <fmanola@acm.org>
Date: Mon, 9 Feb 2009 11:01:05 -0500
Cc: SWIG <semantic-web@w3.org>
Message-Id: <245A9C9C-4AA9-43A7-B344-F68965551424@acm.org>
To: paola.dimaio@gmail.com

On Feb 8, 2009, at 11:16 PM, paola.dimaio@gmail.com wrote:

> I agree with everything that you say below but your conclusion
> The point is that some things (or aspects of those things), even if  
> they change, aren't necessarily going to change fast enough so that  
> assuming they're reasonably static generates significant errors (in  
> whatever).
> also leads to infer that  'some other things' (the ones not included  
> in your 'some' above) may well change fast (and time being relative,  
> fast could be any length of time)
> The way I see it (could be wrong) is that URIs are going to be  
> fixed, but they point to resources (definitions) that can change
> If I understand this right, the uri to a web page will stay the  
> same, even when I update the page content, (is that so?)
> The problem perhaps arises when we do not update/maintain the page  
> (say that contains a definition) then the uri points to something  
> outdated and thus, results in being misleading
> If we need to use the 'open  web' to do any level of reasoning, then  
> the resources should be reasonably updated, otherwise the result of  
> the reasoning iver several resources that may be marginally out of  
> date may end up be  skewed (not screwed) , although I agree that  
> depending on their volatility the degree  and weight of the skew may  
> change
> (what blows my mind completely though, is that change always happens  
> in relation to something else that also changes, and somehow it  
> looks like our ability to make our representations adaptive and  
> evolutionary is still a tad away from our immediate ability due to  
> our lack of understanding of the causal dependencies between  
> different factors)
> feel free to correct me


If I understand what you say above, I don't think it's entirely  
correct.  Specifically, I don't think the relationship between URIs  
and what they point to is as straightforward as you seem to be  
saying.  While it's true that you can have a URI that points to a  
resource (like a definition) that changes, you can also have a URI  
that points to a resource (like the same definition) as of a specific  
point in time (or as in some non-temporal context).  You'd want these  
to be distinct URIs because they refer to different resources (one is  
"the current definition of X" and the other is "the definition of X as  
of Y".  The Architecture of the World Wide Web" (http://www.w3.org/TR/webarch/ 
) describes an example that illustrates this.  Section 2.3.2 says "In  
this story, there are two resources: “a report on the current weather  
in Oaxaca” and “a report on the weather in Oaxaca on 1 August 2004”.  
The managers of the Oaxaca weather site assign two URIs to these two  
different resources. On 1 August 2004, the representations for these  
resources are identical.  That fact that dereferencing two different  
URIs produces identical representations does not imply that the two  
URIs are aliases."  The URIs that point to W3C specifications  
illustrate the same idea.  There is one URI that always refers to the  
"latest version", and separate URIs for each dated version.  As of a  
given date, there will be a pair of URIs that return the same  
representation, but the two URIs refer to different resources.

As far as the other points are concerned, it's certainly true that we  
have to deal with changing definitions (and data) in the Semantic Web,  
and that this complicates things. I don't think this is exactly an  
insurmountable task.  Of course, we have to take time (and other  
contexts in which things can change) more explicitly into account, and  
maintain more metadata to describe those contexts, but we already have  
to do this in some circumstances.  For example, in an operational  
database we tend to expect the definitions to remain static and the  
data to be the latest available, but in a database containing  
historical information we have to deal explicitly with time, both in  
the form of different data values (at different times) for the same  
item, and potentially in the form of different definitions for the  
items (the same holds true in merging heterogeneous databases).  All  
this complicates things, but that's part of dealing with change, and  
it's not really a new problem.  The Semantic Web just forces us to  
face the problem more directly.  At least that's MHO.


> On Mon, Feb 9, 2009 at 12:00 AM, Frank Manola <fmanola@acm.org> wrote:
> All this seems reasonable enough, but we also need to remember that  
> in these respects the SW isn't going to be all that different from  
> lots of other "representations" that we use and rely on all the time  
> (databases, maps, books, etc.), and which are perfectly reasonable  
> representations of what the purport to depict for most purposes.   
> Using your example, a map may not be the territory, and we need to  
> have in the backs of our minds the fact that things may have changed  
> since the map was made (or that the map is inaccurate in some  
> respect), but that doesn't mean we don't rely a lot on maps and find  
> them extremely useful.  Moreover, since we know we're going to rely  
> on maps being a good representation of the territory (that's what we  
> make them for), part of the "engineering" that goes into them  
> involves making them as reliable as possible, and keeping them up to  
> date.  It also involves creating artifacts like benchmarks that we  
> specifically try to make sure stay where they were when the map was  
> created, while everything else is changing independently (benchmarks  
> can move, or disappear too, but we make specific efforts to reduce  
> those occurrences), to act as reference points.  We also recognize  
> (and tend to rely on) that things depicted on the map change at  
> different rates, and to different extents.  For example, when  
> looking at a highway map, I'm apt to be a lot more ready to believe  
> that a bridge along the route between Philadelphia and Baltimore has  
> been torn down since the map was created than to believe that  
> Philadelphia has disappeared (or moved into New Jersey).  The point  
> is that some things (or aspects of those things), even if they  
> change, aren't necessarily going to change fast enough so that  
> assuming they're reasonably static generates significant errors (in  
> whatever).
> --Frank
Received on Monday, 9 February 2009 16:01:46 UTC

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